This invention relates to an electronic flash apparatus, and more particularly to a display device for indicating whether or not the flash tube of the electronic flash apparatus has been fired and whether or not the resultant flash lighting is sufficient for making a correct exposure as the object-to-camera is very large.
It is known to provide electronic flash apparatus of the type in which when the amount of light reflected from an object being photographed with flash illumination has reached a predetermined level, a switching element connected in series to a flash tube is turned to the off state to interrupt the discharging through the flash tube, as disclosed in British Pat. No. 1,376,880.
It is also known to incorporate into such a type of electronic flash apparatus a display device for indicating whether or not the flash tube has been fired. According to British Pat. No. 1,376,880, this device is constructed from a display element such as a neon lamp connected in parallel with a main capacitor for storing an electrical energy which is to be discharged through the flash tube to convert the electrical energy to a flash light energy.
With such a display device of the electronic flash apparatus, however, when an object being photographed is at a relatively short distance from the camera with the flash apparatus, the amount of electrical energy discharged from the main capacitor through the flash tube is so small that the voltage across the main capacitor does not drop largely enough to extinguish the display element despite of the fact that the flash tube has been fired, thus the display element being held in continuous lighting. As a result, the operator would be apprised as if the flash tube remains unfired, though the reverse is the case.
Further, the conventional display device for the electronic flash apparatus though having a function of indicating whether or not the flash tube has been fired even when the object is at a long distance is incapable of informing the operator of whether or not the correct exposure has been made on the photographic film associated with the camera under the resultant flash lighting condition as the object-to-camera distance is very long. For this reason, the photographer is apt to mistake the resultant flash exposure for the correct one.